The present relates to a method and a system of switching-over from a regular communication control processor (hereinafter abbreviated to "CCP") connected to a plurality of host computers to a backup CCP, and particularly relates to a method and a system of automatically switching-over from a regular CCP to a backup CCP in case of failure of the regular CCP.
A system having regular and backup CCPs connected to a plurality of host computers has been disclosed in HITAC manual "Program Product VOS3 Communication Management XNF, Introduction and Practical Use", 8090-3-172, 63-7 (1988), Hitachi, Ltd. One program is stored in both the regular and backup CCPs before a link state is established between the regular CCP and the respective host computers. In case of failure of the regular CCP in the system, all the communication lines connected to the regular CCP are manually switched over to the backup CCP through a line switch. Then, an operator command is issued from the respective host computers to release the link state established between the regular CCP and the respective host computers and establish a new link state between the backup CCP and the respective host computers to thereby perform switching-over for the regular CCP to the backup CCP (Prior Art 1).
On the other hand, a communication system in which dual-system CCPs are connected to each other through health check lines has been disclosed as "Load Distributed Communication Control Processor" in JP-A-6354846. In the system, one CCP monitors the state of the other CCP so that, in case of failure of one CCP, the communication line connected to the failure CCP is connected to the other CCP (Prior Art 2).
Now consider the case where the Prior Art 1 is applied to a communication system having a plurality of host computers operated on the basis of one program and separated into one master host computer and slave host computers, two CCPs of the same hardware construction separated into a regular CCP connected to the respective host computers to be operated on the basis of the program and a backup CCP, and a line switch for collectively switching lines between the two CCPs. In case of failure of the regular CCP, a long time is required for recovery from the failure because operator commands must be issued from all of the host computers connected to the new regular CCP which is changed from a backup CCP into a regular CCP (that is, human thought and operation must be used).
On the other hand, in the case where the Prior Art 2 is employed, health-check lines must be provided between the regular CCP and the backup CCP, so that wasteful physical resources are required. Further, it is necessary to newly provide a technique for informing the host computers that the CCP to be connected to the host computers should be a backup CCP.